This invention relates to a circuit board and a sealing structure, and more particularly to a technique which is effectively applicable to selective removal and cleaning of a layer of a material such as a high polymer material or an organic material in a circuit board or a sealing structure.
It is known that, in a ceramic circuit board or the like used for mounting or sealing a semiconductor integrated circuit element, a thin film or layer of, for example, a high polymer material such as a polyimide resin is used for inter-layer insulation in a multilayer interconnection wiring arrangement provided on the circuit board or used as a protective film or layer for such a multilayer interconnection wiring arrangement.
This thin layer of the high polymer material such as polyimide is formed by coating the material in liquid form on the entire surface of the board by means such as spin-coating and then thermally setting or hardening the coating. Therefore, it becomes necessary to selectively remove, prior to the later step of soldering or plating, the polyimide layer where it covers, for example, a metallized pattern formed in an external connection terminal region of the interconnection wiring arrangement or a metallized pattern formed in a region where the package is sealed by a cap.
Hitherto, etching, for example has been dry etching commonly employed in the art as a means for selectively removing such a layer of a high polymer material.
According to this dry etching, plasma of, for example, oxygen gas is directed toward and onto the entire surface of a ceramic board where such a thin layer of a high polymer material is masked by, for example, a mask of a metal material, so as to selectively etch the thin layer of the high polymer material by bombardment with ions or electrons.
Another method is disclosed in, for example, JP-A-62-145797. According to this disclosed method, a polyester film covering a copper foil pattern deposited on a flexible circuit board is selectively removed by irradiating the film with an ultraviolet laser beam so as to externally expose a region such as an external terminal region of the copper foil pattern.